Spring 配置类不可以用@Component代替

1. 现象

@Configuration 和@Component 的元注解一样的， 那么功能一样吗， 能用@Component标注测试类吗？不行

@Configuration 会被标记为Full模式代理，被cglib进行代理
@Component按Lite模式处理

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface Configuration {}

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Indexed
public @interface Component {}

2. 测试

public class Dog {
}
@Getter
@Setter
public class Student {
    private Dog dog;
}

（1）Configuration

@Configuration
public class StudentConfig {

    @Bean
    public Dog dog() {
        Dog dog = new Dog();
        System.out.println("dog = " + dog);
        return dog;
    }

    @Bean
    public Student student() {
        Student student = new Student();
        student.setDog(dog());
        System.out.println("student.getDog() = " + student.getDog());
        return student;
    }
}

结果： student.setDog(dog());用的是容器中的dog.
dog = com.ityj.ssm.etity.Dog@4f6b687e
student.getDog() = com.ityj.ssm.etity.Dog@4f6b687e

（2）Component

@Component
public class StudentConfig {
}

结果： student.setDog(dog());用的是自己new出的dog
dog = com.ityj.ssm.etity.Dog@74dbb1ee
dog = com.ityj.ssm.etity.Dog@3efedc6f
student.getDog() = com.ityj.ssm.etity.Dog@3efedc6f

3. 源码

（1）标记@Configuration为Full模式

org.springframework.context.annotation.ConfigurationClassUtils#checkConfigurationClassCandidate

（2）进行增强

org.springframework.context.annotation.ConfigurationClassPostProcessor#postProcessBeanFactory
org.springframework.context.annotation.ConfigurationClassPostProcessor#enhanceConfigurationClasses